Insight User Guide: Natural ground subsidence
The natural ground subsidence section is based on the BGS GeoSure dataset. It is produced for use at 1:50,000 scale providing a 50m ground resolution. Each category is rated on a 6 tiered scale with the following ratings: No data, Negligible, Very Low, Low, Moderate and High.
Shrink-swell clays
The potential hazard presented by soils that absorb water when wet (making them swell), and lose water as they dry (making them shrink). This shrink-swell behaviour is controlled by the type and amount of clay in the soil, and by seasonal changes in the soil moisture content (related to rainfall and local drainage).
| A - Negligible | Ground conditions predominantly non-plastic. |
| B - Very low | Ground conditions predominantly low plasticity. |
| C - Low | Ground conditions predominantly medium plasticity. |
| D - Moderate | Ground conditions predominantly high plasticity. |
| E - High | Ground conditions predominantly very high plasticity. |
Data source: British Geological Survey
Data update schedule: Quarterly
Running sands
The potential hazard presented by rocks that can contain loosely-packed sandy layers that can become fluidised by water flowing through them. Such sands can ‘run’, removing support from overlying buildings and causing potential damage.
| A - Negligible | No indicators for running sand identified. |
| B - Very low | Slight potential for running sand problems only possible if water table rises. |
| C - Low | Possibility of running sand problems after major changes in ground conditions. |
| D - Moderate | Significant potential for running sand problems with relatively small changes in ground conditions. |
| E - High | Very significant potential for running sand problems. |
Data source: British Geological Survey
Data update schedule: Quarterly
Compressible deposits
The potential hazards presented by natural deposits that could compress when a load (such as a building) is placed on them or they become saturated with water.
| A - Negligible | No indicators for compressible deposits identified. |
| B - Very low | Very slight potential for compressible deposits to be present. |
| C - Low | Slight possibility of compressibility problems. |
| D - Moderate | Significant potential for compressibility problems. |
| E - High | Very significant potential for compressibility problems. |
Data source: British Geological Survey
Data update schedule: Quarterly
Collapsible deposits
The potential hazards presented by natural deposits that could collapse when a load (such as a building) is placed on them or they become saturated with water.
| A - Negligible | Deposits with potential to collapse when loaded and saturated are believed not to be present. |
| B - Very low | Deposits with potential to collapse when loaded and saturated are unlikely to be present. |
| C - Low | Deposits with potential to collapse when loaded and saturated are possibly present in places. |
| D - Moderate | Deposits with potential to collapse when loaded and saturated are probably present in places. |
| E - High | Deposits with potential to collapse when loaded and saturated are present. |
Data source: British Geological Survey
Data update schedule: Quarterly
Landslides
The potential for landsliding (slope instability) to be a hazard assessed using 1:50,000 scale digital maps of superficial and bedrock deposits, combined with information from the BGS National Landslide Database and scientific and engineering reports.
| A - Negligible | No indicators for slope instability identified. |
| B - Very low | Slope instability problems are unlikely to be present. |
| C - Low | Possibility of slope instability problems after major changes in ground conditions. |
| D - Moderate | Significant potential for slope instability with relatively small changes in ground conditions. |
| E - High | Very significant potential for slope instability. Active or inactive landslides may be present. |
Data source: British Geological Survey
Data update schedule: Quarterly
Ground dissolution of soluble rocks
The potential hazard presented by ground dissolution, which occurs when water passing through soluble rocks produces underground cavities and cave systems. These cavities reduce support to the ground above and can cause localised collapse of the overlying rocks and deposits.
| A - Negligible | Soluble rocks are either not thought to be present, or are not prone to dissolution. Dissolution features are unlikely to be present. |
| B - Very low | Soluble rocks are present but unlikely to cause problems except under exceptional conditions. |
| C - Low | Significant soluble rocks are present. Low possibility of localised subsidence or dissolution related-degradation of bedrock occurring naturally, but may be possible in adverse conditions such as high surface or subsurface water flow. |
| D - Moderate | Very significant soluble rocks are present with a moderate possibility of localised natural subsidence or dissolution-related degradation of bedrock, especially in adverse conditions such as concentrated surface or subsurface water flow. |
| E - High | Very significant soluble rocks are present with a high possibility of localised subsidence or dissolution-related degradation of bedrock occurring naturally, especially in adverse conditions such as concentrated surface or subsurface water flow. |
Data source: British Geological Survey
Data update schedule: Quarterly